Dihydroxylation, and

Jones and Vogel investigated the snbstitnent effect of a 5,6-bis(methoxycarbonyl) group in bicyclo[2.2.2]octene (48i) [117]. The substituent effect of a single 5-exo substituent on the facial selectivities of bicyclo[2.2.2]octenes 48b-48h was also characterized by our group [118]. Epoxidation and dihydroxylation of the olefin moiety of 5-exo-substituted... 

Epoxidation and dihydroxylation of the olefin moiety of 2-substituted dibenzobicy-clo[2.2.2]octatrienes (71) were studied [103, 104]. 

The iyn-preference of 105b and 105c is similar to those observed in the reduction of the related ketones, 34 and in the epoxidation and dihydroxylation of the related olefins 71 [104]. Although the trajectories of the attacking reagents are considered to be different in these reactions [83-87, 170, 171], all three types of reactions favor iyn-addition, which excludes a predominant role of divergent trajectories in these dibenzobicyclic systems. 

Dioxygenases usually contain a tightly bound iron atom and catalyze hydroperoxidation of allylic molecules or carboxylic acids, and dihydroxylation of aromatics (Figure 1.5) [33]. 

It is now clear that pure pheromones can be synthesized in quantity. The problem is how to prepare them simply and efficiently. New synthetic methodologies are always welcome to improve the existing syntheses. Organoborane reactions and organotransition metal chemistry contributed much to improve the efficiency of carbon-carbon bond formation, while asymmetric epoxidations and dihydroxylations as well as enzymatic reactions greatly improved the enantiomeric purity of synthetic pheromones. 

Lindel and co-workers had earlier achieved cyclization of intermediate 166 with 2-iodoxybenzoic acid (IBX, Dess-Martin periodinane) to give 167 (Equation 41), followed by subsequent dehydration and dihydroxylation of G(10)—C(10zz) to an advanced synthetic intermediate <2002TL3699>. 

The oxidation of enol ethers and their derivatives is a useful method for the synthesis of a-hydroxy-ketones or their derivatives, which are versatile building blocks for organic synthesis. Since enol ethers and esters are types of olefin, some asymmetric epoxidation and dihydroxylation reactions have been applied to their oxidation. 

An analysis of the processes listed in Table 37.2 shows that asymmetric hydrogenation of C=C and C=0 functions is by far the predominant transition metal-catalyzed transformation applied for industrial processes, followed by epoxida-tion and dihydroxylation reactions. On the one hand, this is due to the broad scope of catalytic hydrogenation, and on the other hand it could be attributed to... 

To give a better understanding of the scope of application for epoxidation and dihydroxylation reactions in organic synthesis, the studies by several groups on these reactions are discussed in the remainder of this section. 

In 1959, Kharasch et al.43 reported an allylic oxyacylation of olefins. In the presence of f-butyl perbenzoate and a catalytic amount of copper salt in refluxing benzene, olefin was oxidized to allyl benzoate, which could then be converted to an allyl alcohol upon hydrolysis. It is desirable to introduce asymmetric induction into this allylic oxyacylation because allylic oxyacylation holds great potential for nonracemic allyl alcohol synthesis. Furthermore, this reaction can be regarded as a good supplement to other asymmetric olefinic reactions such as epoxidation and dihydroxylation. 

Stereoselective intramolecular oxymercuration of carbohydrate derivatives was proposed as the key reaction for efficient preparation of mono- and dihydroxylated unsymmetrical bis-tetrahydrofuran skeletons present in naturally occurring biologically active acetogenins. The trans- and. mz-selective intramolecular oxymercurations were explored in an enantioselective synthesis of the bis-tetrahydrofuran skeleton of mucoxin (Fig. 57).73... 

H ASYMMETRIC EPOXIDATION AND DIHYDROXYLATION OF OLEFINIC DOUBLE BONDS... 

Since the first two approaches are very well known and exploited, and excellent reviews and books on the topic are available [1], we will deal only with some of the most recent findings in chemical catalysis -excluding the Sharpless asymmetric epoxidation and dihydroxylation, to which the whole of Chapter 10 is devoted. Synthetic catalysts which mimic the catalytic action of enzymes, known as chemzymes, will be also considered. 

From the point of view of efficiency and application to the industrial production of optically pure compounds the chiral catalyst procedure is the methodology of choice. In this context. Sharpless asymmetric epoxidation and dihydroxylation, Noyori-Takaya s second generation asymmetric hydrogenations and Jacobsen s epoxidation [3] have had a tremendous impact in the last few years and they constitute the basis of the newly spawned "chirotechnology" firms, as well as of the pharmaceutical, fine chemical and agriculture industries. 

The chapter on alicyclic stereoselection has been splitted in two chapters (9 and 10). Chapter 10, which is exclusively devoted to Sharpless asymmetric epoxidation and dihydroxylation, has been rewritten de novo. The most recent advances in catalytic and stereoselective aldol reactions are incorporated in Chapter 9. 

Numerous unidentified B, C and D-ring mono- and dihydroxylation products... 

Polyurethane energetic block copolymers, (VIII), consisting of toluene diisocyanate, 1,4-butanediol, and dihydroxyl poly(3-azidomethyl-3-methylox-etane) were prepared by Sanderson et al. (3) and used as binders in high-energy compositions, especially rocket propellants. Poly(glycidyl nitrate) urethanes were previously prepared by the authors and are discussed (4). 

The enantioselective oxygenation procedures, epoxidation and dihydroxylation, developed by Barry Sharpless have dominated single-enantiomer organic synthesis. Recently, several additional methods for enantioselective oxidation have been developed, based on the a-functionalization of carbonyl compounds. 

These findings were also in contrast to the results they obtained carrying out the bioconversion of nerolidol with Aspergillus niger [135,136]. In this case, the two main metabolites identified were 12-hydroxynerolidol (159) and 10,11-dihydroxynerolidol (160). The same reactions were noticed when dihydronerolidol was used as substrate co-methyl hydroxylation and dihydroxylation of the remote double bond. 

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